Apparatus and a process for inductively heating workpieces

ABSTRACT

Method and apparatus for inductively heating workpieces, particularly those that are, or are substantially, bodies of revolution by supplying current to a least single conductor loop adjacent the workpiece. In the embodiment described below, current from two suitable sources is supplied to the loop at different points so that heating can be controlled satisfactorily at different locations on the workpiece. According to one aspect of the invention, the currents are supplied at different phases and further one of the sources is connected to the loop by an additional heating conductor.

[151 3,684,851 [451 Aug. 15, 1972 United States Patent Reinke et a1.

Eitainirier-J. V. Truhe Assistant Examiner-Hugh D. J aeger Attomey-Cushman, Darby & Cushman [54] APPARATUS AND A PROCESS FOR INDUCTIVELY HEATING WORKPIECES [72] Inventors: Friedhelm Reinke,

Oelingrath; Karl lsyirchen, both of ABSTRACT Frisch, Werme Germany [73] Assignee: AEG-Elotherm GmbH, Remscheid- Method and apparatus for inductively heating workpieces, particularly those that are, or are substantially, bodies of revolution by supplying current to a least single conductor loop adjacent the workpiece. In the embodiment described below, current from two suitable sources is supplied to the loop at difi'erent points so that heating can be controlled satisfactorily at different locations on the workpiece. According to one aspect of the invention, the currents are supplied at Hasten, Germany [22] Filed: Nov. 27, 1970 [21] Appl. No.: 92,980

[30] Foreign Application Priority Data Dec. 18, 1969 Germany..........P 19 63 368.2

[52] US. Cl. ..........219/l0.43, 219110.75, 219/1077 different phases and further one of the sources is connected to the loop by an additional heating conductor.

[51] Int. 5/00, HOSb 9/06 219/85, 10.43, 10.79, 10.75,

[58] Field of l4Clains,5DrawingHgures [56] References Cited UNITED STATES PATENTS 2,655,590 10/1953 Gardner...... .......2l9/10.75

PATENTEDAUBISIQYZ 3.684.851

SHEET 1 0F 3 ,QFA 2 16/56 ZZ WM PATENTED M18 15 m2 SHEET 3 BF 3 a M mm mi M Z Z APPARATUS AND A PROCESS FOR INDUCTIVELY HEATING WORKPIECES The invention relates to a method and apparatus for inductively heating workpieces, particularly for surface hardening workpieces which are, or substantially are, bodies of revolution. The invention is particularly satisfactory with workpieces which comprise a shaft portion and a portion having a diameter larger than the shaft portion, e.g. a rear axle half shaft of a motor vehicle, and particularly relates to apparatus for carrying out such inductive heating of the type in which the inductor comprises two heating conductors extending substantially in the direction of the workpiece axis and interconnected adjacent the larger diameter part of the workpiece to complete a heating current through an associated pair of feeders from an alternating current generator.

Apparatus of this kind is described in generally French Pat. No. 1,553,475. Such apparatus is advantageously used for inductively surface hardening workpieces, such as the rear axle half shafts of motor vehicles, which consist of an elongated shaft provided at one end with a flange and formed with a fillet where shaft and flange meet. The surface layer that is to be hardened extends over the major part of the shaft, the fillet and part of the adjoining surface of the flange. The desired local depth of the hardened layer in different parts 'of the workpiece is achieved by appropriately selecting the corresponding width of the coupling gap, the laminations mounted on the heating conductor loop of the inductor and the general geometry of the heating conductor loop. Further, arrangements of this kind are principally used in apparatus for inductively surface-hardening workpieces in which relative motion between inductor and workpiece normal to the workpiece axis is necessary in order to bring the inductor into the required working position in relation to the workpiece, or vice versa.

However, one disadvantage of such conventional arrangements is that the part of the heating conductor that heats up the fillet is practically limited in length to not more than an arc of 180 around the circumference of the work. This arc distance is often insufficient for generating the required temperature distribution in the fillet and flange.

In order to overcome this difficulty it has previously been proposed that the heating inductor include at least two electrically separate and complete, current carrying, conductor loops. However, this approach is unsatisfactory unless the spatial conditions prescribed by the geometry of the workpiece permit two such heating conductor loops to be arranged so that they are capable of generating a non-anomalous temperature distribution. In the region of overlap of the two heating conductor loops this is usually difiicult to accomplish.

Accordingly, the novel invention of this application, as set forth below, relates to a method and apparatus for inductively heating workpieces that are, or are substantially, bodies of revolution, without incurring the shortcomings of conventional apparatus previously proposed for the purpose. This is accomplished by providing at least one additional input for heating current to a heating conductor loop such as employed in the heating devices discussed briefly above. In addition to a first pair of feeders which connect a first current source to the loop, a second pair of feeders links a second current source to the loop via at least two suitable connections, and switch means supply the inductor with heating current through both pairs of feeders simultaneously or only through one pair of feeders.

When both pairs of feeders operate simultaneously the relative phase position of the heating currents fed to the inductor is preferably chosen so that the heating current in that part of the heating conductor loop which begins at one of the connections to the loop and extends to the other pair of feeders is less than when only one current source is supplying current to the loop, and is greater in the other part of the loop. That part of the heating conductor loop which begins at the second input for heating current and extends to the first input preferably has a substantially higher impedance than the other part of the heating conductor loop which begins at the same input.

According to another useful feature of the invention the connections of the second pair of feeders are preferably located on the heating conductors that extend substantially in the direction of the workpiece axis. Furthermore, in a preferred embodiment of the invention at least one of the feeders to the connections of the second heating current input forms an additional heating conductor element extending over the surface of the workpiece.

The invention of this application can also be used satisfactorily for inductively heating workpieces that are substantially elongate bodies of revolution, including bodies that have an approximately constant diameter, whenever it is desired to generate different temperature distributions in different zones of the workpieces, such as zones of different depths of heat pentration.

Many other objects and purposes of the invention will become clear from the following detailed description of the invention.

Embodiments of the invention are hereinafter described and illustrated in the accompanying drawings, in which:

FIG. 1 is a schematic representation of the essential parts of one embodiment of apparatus according to the invention;

FIG. 2 shows a circuit schematic for supplying current to the apparatus of FIG. 1

FIG. 3 shows a schematic of a working station for hardening a workpiece,

FIG. 4 shows a half shaft workpiece, and

FIG. 5 shows an apparatus for inductively heating the workpiece of FIG. 4.

Referring to FIG. 1, a workpiece l to be hardened, in this instance a rear axle half shaft for a motor vehicle, is shown mounted between centers 2 which can conventionally impart rotation to the workpiece during heating. For the purpose of understanding the invention of this application, it is assumed the surface of the shaft 3, the fillet 4 at the base of the flange 5 and a portion of the surface of the flange are to be hardened.

For inductively heating workpiece 1, an inductor 6 is provided of which only the current-carrying parts are shown for the sake of clarity. The inductor 6 comprises two substantially parallel heating conductors 7 which extend in the direction of the workpiece axis, and which at the ends facing the flange 5 are interconnected by an arcuate conductor element 8 to complete a heating conductor loop. The end of this loop at the other end of the shaft 3 is connected by closely adjacent feeders 9 and another arcuate conductor element 10 to the output of a conventional heating transformer 11. Where the heating conductors 7 are cross connected by arcuate element 8 they are provided with connections for a second current input which permits heating current to be provided through two further feeders 14 from a second conventional heating current transformer 13. One of these feeders 14 includes an additional heating element 15 which extends over the surface of the workpiece flange 5.

One suitable circuit for feeding the heating currents is schematically shown in FIG. 2 of the drawings. A medium frequency current generator 16 feeds each of two heating current transformers l1 and 13 through switches 19 and 20 which are controlled respectively by time relays l7 and 18. The transformer primaries are bridged in conventional manner by capacitors 21 and 22 for the purpose of reducing reactive loss. The secondaries of the heating current transformers l1 and 13 are connected by feeders 9 and the conductor element 10 and by feeders 14 through an additional element 15 to the main heating conductors 7 and 8.

The workpieces may be conveyed through the several working stations required for performing the hardening process in a manner that is well understood, for instance by a pair of indexable spiders 23, as schematically shown in FIG. 3. The pair of indexable spiders 23 in FIG. 3 comprises three pairs of arms 24 each fitted with a pair of centers 2 for mounting a workpiece at a loading station 25 between the centers and for then conveying it first to a heating station 26 where it is inductively heated, and then to an unloading station 28 which is immersed in a quench 27.

The workpiece 1 that is to be hardened is first taken to the loading station 25 where it is mounted between the centers 2 of one pair of arms of the spiders. The spiders 23 are then indexed 120 to thus convey workpiece 1 to heating station 26 where inductor 6 is advanced into position above the workpiece 1 by an infeeding movement normal to the workpiece axis.

The surface that is to be hardened now begins to be inductively heated. To this end switches 19 and 20 controlled by the time relays 17 and 18 are closed and heating currents from the heating transformers l1 and 13 are fed to the inductor 6. The phase position of the two currents is preferably chosen so that the heating current in the arcuate conductor element 8 will be higher and in the axial heating conductors 7 lower than when current is supplied through only one input. The supplementary heating conductor element 15 operates to preheat flange 5 of workpiece 1.

The part of the heating conductor loop which begins at the connections 12 of the second pair of feeders, and which extends to the heating transformer 11, comprising the axial heating conductors 7, the arcuate conductor element 10 and the feeders 9, preferably has a substantially higher inductance than the other heating conductor loop which begins at these connections 12 and comprises the arcuate conductor element 8. Thus when operating with both current supplying the rise in heating current in the loop which comprises connections 12 and element 8 is substantially greater than the drop in heating current in the axial conductors 7.

Supplying current through two different inputs on the heating conductor loop pennits the temperature distribution in the two heating zones to be independently and readily adjusted to an optimum. In some instances it may be useful at the end of the heating-up time to provide an additional heating period during which the inductor 6 is supplied with current only from one of the two heating current transformers 11 and 13. Since it is possible during the heating-up process to supply the inductor with heating current through both pairs of feeders or only through one of them, the number of available possibilities and accordingly the likelihood of achieving an optimum heating effect in the several surface regions is substantially higher than when using only one pair of feeders, and no modification of the structure or of the geometry of the inductor is required.

After having been inductively heated, the inductor 6 is retracted and the workpiece 1 is taken by another indexing motion of the pair of spiders 23 to the quenching and unloading station 28 which is immersed in the quench 27. After having been quenched the workpiece is released by centers 2 and conveyed therefrom by suitable handling or conveying means.

A modification of the invention is illustrated in FIG. 4 and FIG. 5 of the accompanying drawings wherein a half shaft to be hardened comprises a cylindrical bearing surface 31 of a diameter exceeding that of the shaft, and located between the slightly tapering shaft 29 and a flange 30. In this example, the hardened zone is intended to comprise the entire shaft 39, the bearing surface and part of the fillet 32 between the bearing 31 and the flange 30. For inductively heating this workpiece an inductor 33 such as shown in FIG. 5 is used of which, as in FIG. 1, only the current carrying portions are shown for the sake of clarity.

Inductor 33 comprises two heating conductors 34 which extend substantially in the axial direction of the workpiece and conform with the workpiece contour. In the region of the fillet 32 shown in FIG. 4, these two heating conductors are cross-connected by an arcuate conductor element 35 to form a heating conductor loop which at the other end, as in the embodiment according to FIG. 1, is connected by two closely adjacent feeders 36, directly through an arcuate conductor element 37 and to a heating current supply circuit respectively. At the point where the relatively thin shaft 29 of the workpiece merges into the cylindrical bearing 31 of larger diameter, the two axial heating conductors 34 are provided with connections 38 through which a second heating current supply circuit can feed a heating current through two closely adjacent feeders 39 and an arcuate element 40 forming a supplementary heating conductor element. In this embodiment the relative phase position of the two currents supplied through the two pairs of feeders is preferably such that the heating current in the arcuate conductor element 35 is higher and in the axial heating conductors 34 lower than when current is supplied through only one pair of feeders. This arrangement is operated in a manner analogous to that according to FIG. 1.

It will be appreciated that this invention may be used not only for workpieces comprising a shaft and a part of greater diameter than the shaft but also for workpieces that have a substantially constant diameter, particularly when it is desired to generate in different zones of the workpiece considerably differing temperature distributions, for instance to generate zones in which the heat penetrates to different depths. This may be required when a reduced diameter threaded end of the workpiece is to be hardened through its cross section whereas the remainder of the workpiece is to be only surface-hardened.

Another advantage afforded by the invention is that by feeding the inductor at least at two different points on the heating conductor loop a desired temperature distribution can be achieved even when the coupling gaps between the heating conductors loop and the workpiece are considerable. A wide coupling gap has the advantage of reducing the effect of unavoidable dimensional tolerations of the workpiece on the general heat distribution and of thus ensuring a uniformly maintained constant quality of all the hardened workpieces.

Many changes and modifications of the above embodiments can of course be made without departing from the scope of the invention and accordingly that scope is intended to be limited only by the scope of the appended claims.

What is claimed is:

1. Apparatus for inductively heating a workpiece comprising:

conductor means forming a heating conductor loop for inducing current flow in said workpiece when current is flowing in said conductor loop,

first means connected to said conductor loop at first and second points for supplying current to said conductor loop,

second means connected to said conductor loop at third and fourth points separated from said first and second points for supplying current to said conductor loop, and

means for causing said first and second means to simultaneously supply current to said conductor loop as to supply current through one of said first and second means.

2. Apparatus for inductively heating a workpiece which is at least substantially a body of revolution comprising:

conductor means forming a heating conductor loop for inducing current flow in said workpiece when current is flowing in said conductor loop, including a first conductor extending roughly parallel to the axis of said workpiece, a second conductor extending along the other side of said workpiece roughly parallel to the axis of said workpiece,

first means connected to said conductor means at first and second points for supplying current to said conductor loop,

including a first source of current and means for connecting said first source to one end of said first and second conductors, and

second means connected to said conductor means at third and fourth points separated from said first and second points for supplying current to said conductor loop simultaneously with said first means including said second means includes a second source of current and means for connecting said second source to the other end of said first and second conductors.

3. Apparatus for inductively heating a workpiece comprising:

conductor means comprising a plurality of conductors forming a heating conductor loop for inducing current flow in said workpiece when current is flowing in said conductor loop,

first means connected to said conductor loop at first and second points for supplying current to said conductor loop including an arcuate element having one end connected to said one end of one of said conductors, a first feeder connected to said one end of the other of said conductors and a second feeder connected to the other end of said element and second means connected to said conductor loop at third and fourth points separated from said first and second points for supplying current to said conductor loop simultaneously with said first means, including a second conductor element having one end connected to said other end of one of said conductors, a third feeder connected to said other end of the other of said conductors and fourth feeder means connected to the other end of said element.

4. Apparatus as in claim 3 further including a second arcuate element having one end connected to one of said conductors at said third point and to the other of said conductors at said fourth point.

5. Apparatus as in claim 3 including means for varying the phase relationship between the current supplied from said first source and the current supplied from said second source.

6. Apparatus as in claim 3 wherein said connecting means of said first supplying means includes switch means for connecting and disconnecting said first source means from said first and second points of said conductors and said connecting means of said second supplying means includes switch means for connecting and disconnecting said second source means from said third and fourth points of said conductors.

7. Apparatus as in claim 3 further including indexable workpiece holding means for shifting said workpiece from a position adjacent said conductor means to another position.

8. A method of inductively heating a workpiece comprising the steps of:

supplying a first current to a conductor loop adjacent said workpiece at first and second locations, and supplying simultaneously a second current to said conductor loop at third and fourth locations separate from said first and second locations.

9. A method as in claim 8 further including the step of varying the phase between said first and second currents.

10. In apparatus for inductively heating workpieces that are, or are substantially, bodies of revolution having a larger diameter and part having an inductor comprising two heating conductors extending substantially in the direction of the workpiece axis and interconnected adjacent said larger diameter part of theworkpiece to form a heating conductor loop and an altemating current generator for supplying current to said loop through an associated pair of heating current feeders, the improvement wherein said loop includes at least one second input for heating current through two connections on said heating conductor loop, a second pair of feeders to said connections and switch means whereby the inductor can be supplied with heating current through both pairs of feeders simultaneously.

11. In apparatus as in claim 10, the further improvement wherein the relative phase position of the heating currents fed to the inductor when both pairs of feeders operate simultaneously is chosen so that the heating current in that part of the heating conductor loop which begins at said connections and extends to the other pair of feeders is less than when only one pair of feeders operates, and is greater in the other part of the loop.

12. Apparatus as in claim 11, in which that part of the heating conductor loop which begins at the second heating current input and extends to the first heating current input has a substantially higher impedance than the other part of the heating conductor loop which begins at the same input.

13. Apparatus as in claim 12, in which the connections of the second pair of feeders are located on the heating conductors that extend substantially in the direction of the workpiece axis.

14. Apparatus as in claim 13, in which at least one of the pair of feeders to the connections of the second 10 input forms an additional heating conductor loop extending over the surface of the workpiece. 

1. Apparatus for inductively heating a workpiece comprising: conductor means forming a heating conductor loop for inducing current flow in said workpiece when current is flowing in said conductor loop, first means connected to said conductor loop at firsT and second points for supplying current to said conductor loop, second means connected to said conductor loop at third and fourth points separated from said first and second points for supplying current to said conductor loop, and means for causing said first and second means to simultaneously supply current to said conductor loop as to supply current through one of said first and second means.
 2. Apparatus for inductively heating a workpiece which is at least substantially a body of revolution comprising: conductor means forming a heating conductor loop for inducing current flow in said workpiece when current is flowing in said conductor loop, including a first conductor extending roughly parallel to the axis of said workpiece, a second conductor extending along the other side of said workpiece roughly parallel to the axis of said workpiece, first means connected to said conductor means at first and second points for supplying current to said conductor loop, including a first source of current and means for connecting said first source to one end of said first and second conductors, and second means connected to said conductor means at third and fourth points separated from said first and second points for supplying current to said conductor loop simultaneously with said first means including said second means includes a second source of current and means for connecting said second source to the other end of said first and second conductors.
 3. Apparatus for inductively heating a workpiece comprising: conductor means comprising a plurality of conductors forming a heating conductor loop for inducing current flow in said workpiece when current is flowing in said conductor loop, first means connected to said conductor loop at first and second points for supplying current to said conductor loop including an arcuate element having one end connected to said one end of one of said conductors, a first feeder connected to said one end of the other of said conductors and a second feeder connected to the other end of said element and second means connected to said conductor loop at third and fourth points separated from said first and second points for supplying current to said conductor loop simultaneously with said first means, including a second conductor element having one end connected to said other end of one of said conductors, a third feeder connected to said other end of the other of said conductors and fourth feeder means connected to the other end of said element.
 4. Apparatus as in claim 3 further including a second arcuate element having one end connected to one of said conductors at said third point and to the other of said conductors at said fourth point.
 5. Apparatus as in claim 3 including means for varying the phase relationship between the current supplied from said first source and the current supplied from said second source.
 6. Apparatus as in claim 3 wherein said connecting means of said first supplying means includes switch means for connecting and disconnecting said first source means from said first and second points of said conductors and said connecting means of said second supplying means includes switch means for connecting and disconnecting said second source means from said third and fourth points of said conductors.
 7. Apparatus as in claim 3 further including indexable workpiece holding means for shifting said workpiece from a position adjacent said conductor means to another position.
 8. A method of inductively heating a workpiece comprising the steps of: supplying a first current to a conductor loop adjacent said workpiece at first and second locations, and supplying simultaneously a second current to said conductor loop at third and fourth locations separate from said first and second locations.
 9. A method as in claim 8 further including the step of varying the phase between said first and second currents.
 10. In apparatus for inductively heating workpieces that arE, or are substantially, bodies of revolution having a larger diameter and part having an inductor comprising two heating conductors extending substantially in the direction of the workpiece axis and interconnected adjacent said larger diameter part of the workpiece to form a heating conductor loop and an alternating current generator for supplying current to said loop through an associated pair of heating current feeders, the improvement wherein said loop includes at least one second input for heating current through two connections on said heating conductor loop, a second pair of feeders to said connections and switch means whereby the inductor can be supplied with heating current through both pairs of feeders simultaneously.
 11. In apparatus as in claim 10, the further improvement wherein the relative phase position of the heating currents fed to the inductor when both pairs of feeders operate simultaneously is chosen so that the heating current in that part of the heating conductor loop which begins at said connections and extends to the other pair of feeders is less than when only one pair of feeders operates, and is greater in the other part of the loop.
 12. Apparatus as in claim 11, in which that part of the heating conductor loop which begins at the second heating current input and extends to the first heating current input has a substantially higher impedance than the other part of the heating conductor loop which begins at the same input.
 13. Apparatus as in claim 12, in which the connections of the second pair of feeders are located on the heating conductors that extend substantially in the direction of the workpiece axis.
 14. Apparatus as in claim 13, in which at least one of the pair of feeders to the connections of the second input forms an additional heating conductor loop extending over the surface of the workpiece. 